Physical Layer Flashcards
Bit patterns
Signals designating start and end of frame
Three fundamental functions
Data encoding: converting stream of bits into a code
Signaling: the method of representing bits
Physical components: hardware and connectors
Bit time
Each signal has a certain time to occupy media
NRZ
Signaling method suitable for slow speed data links
Code groups
A set of encoded symbols to represent encoded data or control info
Three symbols of code groups
Data symbol
Control symbols: controls transmission
Invalid symbol: not allowed on media
Frequent transitions
Less individual bit errors and less sync loss
Balancing 1s and 0s
DC balancing
Data transfer measured in three ways:
Bandwidth: amount of info flowing from one place to another
Throughput: measure of transfer of bits across media over time
Goodput: transfer of useable data
Crosstalk
Interference in the twisted pairs of wires via their magnetic field
Copper cable
Connects LAN devices to intermediate devices such as routers and switches
Coaxial cable
Consists of a copper conductor surrounded by a layer of flexible insulation
Uses of coaxial
Wireless and cable technologies; most widely used for transporting high radio frequency signals over wire
Fiber optic characteristics
Immune to electromagnetic interference; relatively low signal loss; operated at greater lengths than copper; uses glass or plastic fibers to guide light impulses from source to destination
Single mode optical fiber
Single ray of light emitted usually from a laser; can transmit optical pulses for very long distances; uses subscriber connector
Multimode fiber
Cheaper than single mode; uses Lucent and straight tip connectors; uses led to generate light pulses on the media.
Wireless characteristics
Carry electromagnetic signals at radio and microwave frequencies; performs well in open environments; interference from cordless phones, microwaves, other wireless devices
Wireless networks
802.11 wifi
802.15 wpan Bluetooth
802.16 WiMAX point to multi point topology worldwide interoperability for microwave access
Gsm
Wireless LAN requires
Wireless access point
Wireless NIC adapters
Wireless standards
- 11a 5 ghz 54 Mbps, not interoperable with 802.11b, 802.11g
- 11b 2.4 ghz 11 Mbps have longer range and can penetrate buildings better
- 11g 2.4 ghz 54 Mbps
- 11n 2.4 ghz or 5 ghz 100-200 Mbps 70 m
Fiber optic termination and splicing errors
Misalignment: not precisely aligned to one another
End gap: the media do not completely touch at the splice or connection
End finish: not well polished or dirt is present at termination
Optical time domain reflectometer
Used to test each fiber optic cable segment
Deliver of frames require
Physical media and associated connectors
A representation of bits in media
Encoding of data and control info
Transmitter and receiver circuitry on the network devices
